// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
 *******************************************************************************
 * Copyright (C) 1996-2014, International Business Machines Corporation and    *
 * others. All Rights Reserved.                                                *
 *******************************************************************************
 */
package com.ibm.icu.util;

import com.ibm.icu.impl.CalType;
import com.ibm.icu.impl.EraRules;
import java.util.Date;
import java.util.Locale;

/**
 * <code>JapaneseCalendar</code> is a subclass of <code>GregorianCalendar</code> that numbers years
 * and eras based on the reigns of the Japanese emperors. The Japanese calendar is identical to the
 * Gregorian calendar in all respects except for the year and era. The ascension of each emperor to
 * the throne begins a new era, and the years of that era are numbered starting with the year of
 * ascension as year 1.
 *
 * <p>Note that in the year of an imperial ascension, there are two possible sets of year and era
 * values: that for the old era and for the new. For example, a new era began on January 7, 1989 AD.
 * Strictly speaking, the first six days of that year were in the Showa era, e.g. "January 6, 64
 * Showa", while the rest of the year was in the Heisei era, e.g. "January 7, 1 Heisei". This class
 * handles this distinction correctly when computing dates. However, in lenient mode either form of
 * date is acceptable as input.
 *
 * <p>In modern times, eras have started on January 8, 1868 AD, Gregorian (Meiji), July 30, 1912
 * (Taisho), December 25, 1926 (Showa), and January 7, 1989 (Heisei). Constants for these eras,
 * suitable for use in the <code>ERA</code> field, are provided in this class. Note that the
 * <em>number</em> used for each era is more or less arbitrary. Currently, the era starting in 645
 * AD is era #0; however this may change in the future. Use the predefined constants rather than
 * using actual, absolute numbers.
 *
 * <p>Since ICU4J 63, start date of each era is imported from CLDR. CLDR era data may contain
 * tentative era in near future with placeholder names. By default, such era data is not enabled.
 * ICU4J users who want to test the behavior of the future era can enable this by one of following
 * settings (in the priority order):
 *
 * <ol>
 *   <li>Java system property <code>ICU_ENABLE_TENTATIVE_ERA=true</code>.
 *   <li>Environment variable <code>ICU_ENABLE_TENTATIVE_ERA=true</code>.
 *   <li>Java system property <code>jdk.calendar.japanese.supplemental.era=xxx</code>. (Note: This
 *       configuration is used for specifying a new era's start date and names in OpenJDK. ICU4J
 *       implementation enables the CLDR tentative era when this property is defined, but it does
 *       not use the start date and names specified by the property value.)
 * </ol>
 *
 * <p>This class should not be subclassed.
 *
 * <p>JapaneseCalendar usually should be instantiated using {@link
 * com.ibm.icu.util.Calendar#getInstance(ULocale)} passing in a <code>ULocale</code> with the tag
 * <code>"@calendar=japanese"</code>.
 *
 * @see com.ibm.icu.util.GregorianCalendar
 * @see com.ibm.icu.util.Calendar
 * @author Laura Werner
 * @author Alan Liu
 * @stable ICU 2.8
 */
public class JapaneseCalendar extends GregorianCalendar {
    // jdk1.4.2 serialver
    private static final long serialVersionUID = -2977189902603704691L;

    // -------------------------------------------------------------------------
    // Constructors...
    // -------------------------------------------------------------------------

    /**
     * Constructs a default <code>JapaneseCalendar</code> using the current time in the default time
     * zone with the default locale.
     *
     * @stable ICU 2.8
     */
    public JapaneseCalendar() {
        super();
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> based on the current time in the given time zone
     * with the default locale.
     *
     * @param zone the given time zone.
     * @stable ICU 2.8
     */
    public JapaneseCalendar(TimeZone zone) {
        super(zone);
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> based on the current time in the default time zone
     * with the given locale.
     *
     * @param aLocale the given locale.
     * @stable ICU 2.8
     */
    public JapaneseCalendar(Locale aLocale) {
        super(aLocale);
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> based on the current time in the default time zone
     * with the given locale.
     *
     * @param locale the given ulocale.
     * @stable ICU 3.2
     */
    public JapaneseCalendar(ULocale locale) {
        super(locale);
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> based on the current time in the given time zone
     * with the given locale.
     *
     * @param zone the given time zone.
     * @param aLocale the given locale.
     * @stable ICU 2.8
     */
    public JapaneseCalendar(TimeZone zone, Locale aLocale) {
        super(zone, aLocale);
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> based on the current time in the given time zone
     * with the given locale.
     *
     * @param zone the given time zone.
     * @param locale the given ulocale.
     * @stable ICU 3.2
     */
    public JapaneseCalendar(TimeZone zone, ULocale locale) {
        super(zone, locale);
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> with the given date set in the default time zone
     * with the default locale.
     *
     * @param date The date to which the new calendar is set.
     * @stable ICU 2.8
     */
    public JapaneseCalendar(Date date) {
        this();
        setTime(date);
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> with the given date set in the default time zone
     * with the default locale.
     *
     * @param era The imperial era used to set the calendar's {@link #ERA ERA} field. Eras are
     *     numbered starting with the Tenki era, which began in 1053 AD Gregorian, as era zero.
     *     Recent eras can be specified using the constants {@link #MEIJI} (which started in 1868
     *     AD), {@link #TAISHO} (1912 AD), {@link #SHOWA} (1926 AD), and {@link #HEISEI} (1989 AD).
     * @param year The value used to set the calendar's {@link #YEAR YEAR} field, in terms of the
     *     era.
     * @param month The value used to set the calendar's {@link #MONTH MONTH} field. The value is
     *     0-based. e.g., 0 for January.
     * @param date The value used to set the calendar's DATE field.
     * @stable ICU 2.8
     */
    public JapaneseCalendar(int era, int year, int month, int date) {
        super(year, month, date);
        set(ERA, era);
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> with the given date set in the default time zone
     * with the default locale.
     *
     * @param year The value used to set the calendar's {@link #YEAR YEAR} field, in the era Heisei,
     *     the most current at the time this class was last updated.
     * @param month The value used to set the calendar's {@link #MONTH MONTH} field. The value is
     *     0-based. e.g., 0 for January.
     * @param date The value used to set the calendar's {@link #DATE DATE} field.
     * @stable ICU 2.8
     */
    public JapaneseCalendar(int year, int month, int date) {
        super(year, month, date);
        set(ERA, CURRENT_ERA);
    }

    /**
     * Constructs a <code>JapaneseCalendar</code> with the given date and time set for the default
     * time zone with the default locale.
     *
     * @param year The value used to set the calendar's {@link #YEAR YEAR} time field, in the era
     *     Heisei, the most current at the time of this writing.
     * @param month The value used to set the calendar's {@link #MONTH MONTH} time field. The value
     *     is 0-based. e.g., 0 for January.
     * @param date The value used to set the calendar's {@link #DATE DATE} time field.
     * @param hour The value used to set the calendar's {@link #HOUR_OF_DAY HOUR_OF_DAY} time field.
     * @param minute The value used to set the calendar's {@link #MINUTE MINUTE} time field.
     * @param second The value used to set the calendar's {@link #SECOND SECOND} time field.
     * @stable ICU 2.8
     */
    public JapaneseCalendar(int year, int month, int date, int hour, int minute, int second) {
        super(year, month, date, hour, minute, second);
        set(ERA, CURRENT_ERA);
    }

    // -------------------------------------------------------------------------

    // Use 1970 as the default value of EXTENDED_YEAR
    private static final int GREGORIAN_EPOCH = 1970;

    private static final EraRules ERA_RULES;

    static {
        ERA_RULES = EraRules.getInstance(CalType.JAPANESE, enableTentativeEra());
    }

    /**
     * Check environment variable that enables use of future eras.
     *
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Deprecated
    public static boolean enableTentativeEra() {
        // Although start date of next Japanese era is planned ahead, a name of
        // new era might not be available. This implementation allows tester to
        // check a new era without era names by settings below (in priority order).
        // By default, such tentative era is disabled.
        //
        // 1. System property ICU_ENABLE_TENTATIVE_ERA=true or false
        // 2. Environment variable ICU_ENABLE_TENTATIVE_ERA=true or false
        // 3. Java system property - jdk.calendar.japanese.supplemental.era for Japanese
        //
        // Note: Java system property specifies the start date of new Japanese era,
        //      but this implementation always uses the date read from ICU data.

        boolean includeTentativeEra = false;

        final String VAR_NAME = "ICU_ENABLE_TENTATIVE_ERA";

        String eraConf = System.getProperty(VAR_NAME);
        if (eraConf == null) {
            eraConf = System.getenv(VAR_NAME);
        }

        if (eraConf != null) {
            includeTentativeEra = eraConf.equalsIgnoreCase("true");
        } else {
            String jdkEraConf = System.getProperty("jdk.calendar.japanese.supplemental.era");
            includeTentativeEra = jdkEraConf != null;
        }
        return includeTentativeEra;
    }

    /**
     * @stable ICU 2.8
     */
    @Override
    protected int handleGetExtendedYear() {
        // EXTENDED_YEAR in JapaneseCalendar is a Gregorian year
        // The default value of EXTENDED_YEAR is 1970 (Showa 45)
        int year;
        if (newerField(EXTENDED_YEAR, YEAR) == EXTENDED_YEAR
                && newerField(EXTENDED_YEAR, ERA) == EXTENDED_YEAR) {
            year = internalGet(EXTENDED_YEAR, GREGORIAN_EPOCH);
        } else {
            // extended year is a gregorian year, where 1 = 1AD,  0 = 1BC, -1 = 2BC, etc
            year =
                    internalGet(YEAR, 1) // pin to minimum of year 1 (first year)
                            + ERA_RULES.getStartYear(
                                    internalGet(ERA, CURRENT_ERA)) // add gregorian starting year
                            - 1; // Subtract one because year starts at 1
        }
        return year;
    }

    /**
     * Called by handleComputeJulianDay. Returns the default month (0-based) for the year, taking
     * year and era into account. Defaults to 0 (JANUARY) for Gregorian.
     *
     * @param extendedYear the extendedYear, as returned by handleGetExtendedYear
     * @return the default month
     * @draft ICU 3.6 (retain)
     * @see #MONTH
     */
    @Override
    protected int getDefaultMonthInYear(int extendedYear) {
        int era = internalGet(ERA, CURRENT_ERA);
        // computeFields(status); // No need to compute fields here - expect the caller already did
        // so.

        // Find out if we are at the edge of an era
        int[] eraStart = ERA_RULES.getStartDate(era, null);
        if (extendedYear == eraStart[0]) {
            return eraStart[1] // month..
                    - 1; // return 0-based month
        } else {
            return super.getDefaultMonthInYear(extendedYear);
        }
    }

    /**
     * Called by handleComputeJulianDay. Returns the default day (1-based) for the month, taking
     * currently-set year and era into account. Defaults to 1 for Gregorian.
     *
     * @param extendedYear the extendedYear, as returned by handleGetExtendedYear
     * @param month the month, as returned by getDefaultMonthInYear
     * @return the default day of the month
     * @draft ICU 3.6 (retain)
     * @see #DAY_OF_MONTH
     */
    @Override
    protected int getDefaultDayInMonth(int extendedYear, int month) {
        int era = internalGet(ERA, CURRENT_ERA);
        int[] eraStart = ERA_RULES.getStartDate(era, null);

        if (extendedYear == eraStart[0]) { // if it is year 1..
            if (month == (eraStart[1] - 1)) { // if it is the emperor's first month..
                return eraStart[2]; // return the D_O_M of accession
            }
        }

        return super.getDefaultDayInMonth(extendedYear, month);
    }

    /**
     * @stable ICU 2.8
     */
    @Override
    protected void handleComputeFields(int julianDay) {
        super.handleComputeFields(julianDay);
        int year = internalGet(EXTENDED_YEAR);
        int eraCode =
                ERA_RULES.getEraCode(
                        year, internalGet(MONTH) + 1 /* 1-base */, internalGet(DAY_OF_MONTH));

        internalSet(ERA, eraCode);
        internalSet(YEAR, year - ERA_RULES.getStartYear(eraCode) + 1);
    }

    // -------------------------------------------------------------------------
    // Public constants for some of the recent eras that folks might use...
    // -------------------------------------------------------------------------

    // Constant for the current era.  This must be regularly updated.
    /**
     * @stable ICU 2.8
     */
    public static final int CURRENT_ERA;

    /**
     * Constant for the era starting on Sept. 8, 1868 AD.
     *
     * @stable ICU 2.8
     */
    public static final int MEIJI;

    /**
     * Constant for the era starting on July 30, 1912 AD.
     *
     * @stable ICU 2.8
     */
    public static final int TAISHO;

    /**
     * Constant for the era starting on Dec. 25, 1926 AD.
     *
     * @stable ICU 2.8
     */
    public static final int SHOWA;

    /**
     * Constant for the era starting on Jan. 7, 1989 AD.
     *
     * @stable ICU 2.8
     */
    public static final int HEISEI;

    /**
     * Constant for the era starting on May 1, 2019 AD.
     *
     * @stable ICU 64
     */
    public static final int REIWA;

    // We want to make these era constants initialized in a static initializer
    // block to prevent javac to inline these values in a consumer code.
    // By doing so, we can keep better binary compatibility across versions even
    // these values are changed.
    static {
        MEIJI = 232;
        TAISHO = 233;
        SHOWA = 234;
        HEISEI = 235;
        REIWA = 236;
        CURRENT_ERA = ERA_RULES.getCurrentEraCode();
    }

    /**
     * Override GregorianCalendar. We should really handle YEAR_WOY and EXTENDED_YEAR here too to
     * implement the 1..5000000 range, but it's not critical.
     *
     * @stable ICU 2.8
     */
    @Override
    @SuppressWarnings("fallthrough")
    protected int handleGetLimit(int field, int limitType) {
        switch (field) {
            case ERA:
                if (limitType == MINIMUM || limitType == GREATEST_MINIMUM) {
                    return 0;
                }
                return ERA_RULES.getMaxEraCode(); // max known era, not always CURRENT_ERA
            case YEAR:
                {
                    switch (limitType) {
                        case MINIMUM:
                        case GREATEST_MINIMUM:
                            return 1;
                        case LEAST_MAXIMUM:
                            return 1;
                        case MAXIMUM:
                            return super.handleGetLimit(field, MAXIMUM)
                                    - ERA_RULES.getStartYear(CURRENT_ERA);
                    }
                    // Fall through to the default if not handled above
                }
            default:
                return super.handleGetLimit(field, limitType);
        }
    }

    /**
     * {@inheritDoc}
     *
     * @stable ICU 3.8
     */
    @Override
    public String getType() {
        return "japanese";
    }

    /**
     * {@inheritDoc}
     *
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Override
    @Deprecated
    public boolean haveDefaultCentury() {
        return false;
    }

    /**
     * {@inheritDoc}
     *
     * @stable ICU 4.0
     */
    @Override
    public int getActualMaximum(int field) {
        if (field == YEAR) {
            int era = get(Calendar.ERA);
            if (era == ERA_RULES.getMaxEraCode()) {
                // TODO: Investigate what value should be used here - revisit after 4.0.
                return handleGetLimit(YEAR, MAXIMUM);
            } else {
                int[] nextEraStart = ERA_RULES.getStartDate(era + 1, null);
                int nextEraYear = nextEraStart[0];
                int nextEraMonth = nextEraStart[1]; // 1-base
                int nextEraDate = nextEraStart[2];

                int maxYear = nextEraYear - ERA_RULES.getStartYear(era) + 1; // 1-base
                if (nextEraMonth == 1 && nextEraDate == 1) {
                    // Substract 1, because the next era starts at Jan 1
                    maxYear--;
                }
                return maxYear;
            }
        }
        return super.getActualMaximum(field);
    }

    /**
     * {@inheritDoc}
     *
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Override
    @Deprecated
    protected boolean isEra0CountingBackward() {
        return false;
    }
}
